Blood-Flow Measurements of Injured Peripheral Nerves by Laser Doppler Flowmetry

 

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ABSTRACT

The effects of injury on peripheral nerve blood flow were studied, using a Laserflo® blood perfusion monitor. A total of 11 nerves were studied, five normal and six injured nerves in four patients. Two of the patients had lacerating brachial plexus injuries, and two other patients had compressive neuropathies of their ulnar nerves at the elbow. All of the readings were taken intraoperatively while the patients were undergoing exploration and repair under general anesthesia. Measurements of the damaged nerves were taken serially from the site of injury proximally and distally, by approximating a flexible metric ruler to the dorsal aspect of the nerve along the same axis. In the acutely lacerated injured nerves (3 to 7 days), the measurements were taken at 1, 5,10, and 20 mm. The maximal amount of retraction in any of the nerves was 1 cm; thus, the overall architecture of the nerves was maintained. In the compressed nerves, measurements were taken at 1, 2 and 3 cm proximal and distal to the medial epicondyle.

Measurement of normal undamaged nerves was performed at six different sites along the same axis of the nerve. The averaged results indicate that the normal blood flow ranged from 47 ml/100 g/min to 63 ml/100 g/min, with a mean of 56 ml/100 g/min. In the injured nerves, blood flow was most depressed at sites closest to the laceration, and increased consistently and progressively at sites distant from the injury in both directions. Proximally, blood flow was decreased between 64.2 percent and 81.9 percent at 1 mm; between 37.5 percent and 56.4 percent at 5 mm; between 27.0 percent and 50.3 percent at 10 mm; and between 6.6 percent and 43.4 percent at 20 mm. Distally, blood flow was decreased between 55.5 percent and 86.0 percent at 1 mm; between 24.4 percent and 61.9 percent at 5 mm; between 10.7 percent and 37.5 percent at 10 mm; and between 10.7 percent and 43.7 percent at 20 mm in the acutely injured nerves. In the nerves damaged by chronic compression, the blood flow decreased between 62.6 percent and 65.1 percent at 1 cm; between 58.0 percent and 59.4 percent at 2 cm; and to 43.7 percent at 3 cm proximally. In the distal areas, the decrease in blood flow was found to be between 74.2 percent and 39.8 percent at 1 cm; between 62.5 percent and 24.1 percent at 2 cm; and to 46.5 percent at 3 cm. The data were analyzed using ANOVA and post-hoc analysis.

These preliminary findings indicate that, in addition to the actual penetrating injury, there are marked changes in the regional blood flow of injured nerves. There is a marked reduction in blood flow at sites near the penetrating injury. There is also a marked decrease in peripheral nerve blood flow at the site of compression in the ulnar nerves, with progressive increase in both directions. However, due to the anatomic arrangement of peripheral nerve vasculature, the changes noted in peripheral blood flow cause only regional damage and ischemia, and there is progressive normalization in both proximal and distal directions. This constitutes the first report of intraoperative measurement of peripheral nerve blood flow in humans. Laser Doppler flowmetry may become a useful adjunct in the management of peripheral nerve injuries.